Bottom Line:
BICDR-1 expression is high during early neuronal development and strongly declines during neurite outgrowth.Later during development, BICDR-1 expression is strongly reduced, which permits anterograde secretory transport required for neurite outgrowth.These results indicate an important role for BICDR-1 as temporal regulator of secretory trafficking during the early phase of neuronal differentiation.

ABSTRACTMembrane and secretory trafficking are essential for proper neuronal development. However, the molecular mechanisms that organize secretory trafficking are poorly understood. Here, we identify Bicaudal-D-related protein 1 (BICDR-1) as an effector of the small GTPase Rab6 and key component of the molecular machinery that controls secretory vesicle transport in developing neurons. BICDR-1 interacts with kinesin motor Kif1C, the dynein/dynactin retrograde motor complex, regulates the pericentrosomal localization of Rab6-positive secretory vesicles and is required for neural development in zebrafish. BICDR-1 expression is high during early neuronal development and strongly declines during neurite outgrowth. In young neurons, BICDR-1 accumulates Rab6 secretory vesicles around the centrosome, restricts anterograde secretory transport and inhibits neuritogenesis. Later during development, BICDR-1 expression is strongly reduced, which permits anterograde secretory transport required for neurite outgrowth. These results indicate an important role for BICDR-1 as temporal regulator of secretory trafficking during the early phase of neuronal differentiation.

Mentions:
Most secretory vesicles in neurons exhibit bi-directional motility movements (de Wit et al, 2006). The observed retrograde movement of secretory vesicles in young neurons is likely caused by the interaction between BICDR-1/Rab6 and the dynein–dynactin complex (Figure 4; Supplementary Figure S7), whereas the anterograde movement is most likely explained by the binding of microtubule plus-end-directed kinesin motors. We have shown earlier that kinesin motor kinesin-1/Kif5 associates with BICD and participates in anterograde Rab6 secretory vesicles transport (Grigoriev et al, 2007). Here, we performed a yeast two-hybrid screen for BICDR-1 partners and found Kif1C as a potential interacting protein (Figure 7A). Both full-length BICDR-1 and an N-terminal region of BICDR-1, amino acids 1–353, interact with the C-terminal tail domain of Kif1C, amino acids 811–1090 and not with other tail regions of Kif1C or other kinesin motors, such as Kif5 (Figure 7A; data not shown). This interaction was further supported by co-immunoprecipitation of endogenous Kif1C by overexpressed BICDR-1 in Hela cells (Figure 7B). Moreover, expression of GFP-BICDR-1 in Vero cells and primary neurons caused strong accumulation of endogenous Kif1C at the pericentrosomal region (Figure 7C and D). BICDR-1 expression has no effect on endogenous Kif5 staining (data not shown). These results show that BICDR-1 regulates recruitment and/or activity of the anterograde kinesin motor Kif1C on Rab6 secretory carriers.

Mentions:
Most secretory vesicles in neurons exhibit bi-directional motility movements (de Wit et al, 2006). The observed retrograde movement of secretory vesicles in young neurons is likely caused by the interaction between BICDR-1/Rab6 and the dynein–dynactin complex (Figure 4; Supplementary Figure S7), whereas the anterograde movement is most likely explained by the binding of microtubule plus-end-directed kinesin motors. We have shown earlier that kinesin motor kinesin-1/Kif5 associates with BICD and participates in anterograde Rab6 secretory vesicles transport (Grigoriev et al, 2007). Here, we performed a yeast two-hybrid screen for BICDR-1 partners and found Kif1C as a potential interacting protein (Figure 7A). Both full-length BICDR-1 and an N-terminal region of BICDR-1, amino acids 1–353, interact with the C-terminal tail domain of Kif1C, amino acids 811–1090 and not with other tail regions of Kif1C or other kinesin motors, such as Kif5 (Figure 7A; data not shown). This interaction was further supported by co-immunoprecipitation of endogenous Kif1C by overexpressed BICDR-1 in Hela cells (Figure 7B). Moreover, expression of GFP-BICDR-1 in Vero cells and primary neurons caused strong accumulation of endogenous Kif1C at the pericentrosomal region (Figure 7C and D). BICDR-1 expression has no effect on endogenous Kif5 staining (data not shown). These results show that BICDR-1 regulates recruitment and/or activity of the anterograde kinesin motor Kif1C on Rab6 secretory carriers.

Bottom Line:
BICDR-1 expression is high during early neuronal development and strongly declines during neurite outgrowth.Later during development, BICDR-1 expression is strongly reduced, which permits anterograde secretory transport required for neurite outgrowth.These results indicate an important role for BICDR-1 as temporal regulator of secretory trafficking during the early phase of neuronal differentiation.

ABSTRACTMembrane and secretory trafficking are essential for proper neuronal development. However, the molecular mechanisms that organize secretory trafficking are poorly understood. Here, we identify Bicaudal-D-related protein 1 (BICDR-1) as an effector of the small GTPase Rab6 and key component of the molecular machinery that controls secretory vesicle transport in developing neurons. BICDR-1 interacts with kinesin motor Kif1C, the dynein/dynactin retrograde motor complex, regulates the pericentrosomal localization of Rab6-positive secretory vesicles and is required for neural development in zebrafish. BICDR-1 expression is high during early neuronal development and strongly declines during neurite outgrowth. In young neurons, BICDR-1 accumulates Rab6 secretory vesicles around the centrosome, restricts anterograde secretory transport and inhibits neuritogenesis. Later during development, BICDR-1 expression is strongly reduced, which permits anterograde secretory transport required for neurite outgrowth. These results indicate an important role for BICDR-1 as temporal regulator of secretory trafficking during the early phase of neuronal differentiation.